Recently, with progress of the chemical industry, industrial materials having chemically and physically excellent properties have been demanded in the market. Particularly in the electric/electronic field, a highly purified resin is desired. However, it is recently pointed out that gas (so-called “outgas”), which is vaporized from plastic containers for housing or transporting electric/electronic parts, damages the electric/electronic parts housed in the containers, and that when a resin is molded, the outgas is also generated and contaminates molds, thereby degrading appearance of the resultant molded articles.
Accordingly, highly purified resins such as of polypropylene, polycarbonate and polybutylene terephthalate are used as resins for use in forming wafer boxes used in transportation of semiconductor wafers and so on, chip trays used in transportation or processing of semiconductor chips, or the like. Some resins that are easy to be electrostatically charged often cause electrostatic trouble, and have a limitation to the aforementioned uses.
On the other hand, styrenic resins such as ABS resins have been widely used in the fields of electrics or electronics, household electrical appliances and automobiles, since they are excellent in moldability and physical and mechanical properties. However, styrenic resins also have the above-mentioned problems of outgas generation and electrostatic trouble.
Generally, resins contain residual impurities such as unreacted monomers, oligomers, solvents, compounds blended as auxiliary agents and compounds derived from the auxiliary agents. These impurities are considered to constitute outgas. Therefore, in order to reduce the outgas generation, it is considered that these impurities must be removed. As methods for purifying resins by removing impurities, various methods are known. For example, mention may be made of a method in which volatile substances are stripped from an aqueous dispersion of a polymer substance (see Patent Document 7 below); a method in which monomers are vaporized by dividing latexes into small droplets and supplying them with steam (see Patent Document 8 below); and a method in which heat treatment is carried out under reduced pressure to remove monomers from latexes whilst steam is passed through a tank to form a thin film of steam on the wall surface of the tank (see Patent Document 9 below). However, in these methods, resins are exposed to high temperature for a long time, thereby occasionally decreasing in quality.
On the other hand, as a method for overcoming the problem of electrostatic trouble, kneading an antistatic agent into a resin is generally known. However, this method has a drawback in that the antistatic effect does not last long so that the surface resistivity value increases with time. To improve sustainability of the antistatic effect, a method in which a polyamide elastomer is blended with a styrenic rein such as an ABS resin has been proposed (see Patent Documents 2, 3, 4, and 6 below). It is also known that lithium compounds are used as antistatic agents that can be blended with styrenic resins to further improve antistaticity (see Patent Documents 1 and 5 below).
Although these approaches make it possible to fairly improve the antistaticity of styrenic resins, still higher antistaticity is recently demanded in the electric/electronic field. In addition, a styrenic resin highly reduced in outgas generation is also required. This is the case for resins other than styrenic resins.
Patent Document 1: Japanese Patent Laid-Open No. H05-163402
Patent Document 2: Japanese Patent Laid-Open No. H05-163441
Patent Document 3: Japanese Patent Laid-Open No. H06-107884
Patent Document 4: Japanese Patent Laid-Open No. H06-220274
Patent Document 5: Japanese Patent Laid-Open No. H08-109327
Patent Document 6: Japanese Patent No. 3386612
Patent Document 7: Japanese Patent Laid-Open No. S50-58184
Patent Document 8: Japanese Patent Publication No. S43-6065
Patent Document 9: Japanese Patent Publication No. S44-844